"this week," from vietnam. On edge. With trouble brewing across the globe, from north korea to iran, afghanistan to syria, we're traveling with america's top diplomat, the globe-trotting secretary of state, john kerry. What can he do to keep the peace abroad and keep americans safe at home? And how did his experience in war here in vietnam shape his world view? It's an abc news exclusive. Plus, the republican free for all. I don't care what they do. Are you kidding me? With speaker boehner in all-out-war against the tea party, who will win the fight? Newt gingrich and robert reich join the powerhouse roundtable to break it all done. It's all, right here, this sunday morning. Hello, again. I'm martha raddatz, great to have you with us from ho chi minh city, vietnam. We're here with secretary kerry. Tracking developments here in the region including stunning news in north korea. The leader kim jong-un has executed his uncle and mentor and we're following several other developing stories this morning, including the funeral service for nelson mandela, prince charles and jesse jackson are among the guests for the private ceremony in mandela's home village this morning, capping a ten-day good-bye for the former south african president. &#9834; meanwhile, back here in the city, formerly known as saigon, this is secretary kerry's first trip since he the vietnam vet has taken on his new post, a busy first trip for the son of a foreign officer, now the top american diplomat. Just this week a dramatic shift in syria, is al qaeda gaining ground there? Plus, those alarming new revelations over an american being held in iran. But, we start it off with that shocking move by north korea's young dictator which has rattled governments throughout the region. Mr. Secretary, want to get right to reports to north korea, that the young leader has executed his uncle, his mentor, one of the most powerful people in north korea, what does this tell you about the danger coming from north korea? Well, it tells us a lot about, first of all, how ruthless and reckless he is and it also tells us about how insecure he is, to a certain degree, it tells us a significant amount about the instability internally of the regime, with the numbers of executions. This isn't the first execution, there have been a significant number of executions taking place over the last months which we're aware of, and most importantly, it underscores the importance for all of us of finding a way forward with north korea in order to denuclearize the peninsula. It's an ominous sign of the instability and the danger that exists. What does it tell you about him, we know so little about him? We don't know -- north korea remains relatively opaque, it is not easy, but we do have insights and the insights that we have tell us that he is spontaneous, erratic, still worried about his place in the power structure and maneuvering to eliminate any potential adversary or competitor and does so, obviously ruthlessly -- i mean, you saw the pictures of his uncle being arrested in front of everybody at this -- and this was so public? It really reminded me of a video that we saw of saddam hussein doing the same thing, having people plucked out of the audience, people sitting there sweating and not moving. This is the nature of this ruthless, horrendous dictatorship and of his insecurities. I think we need to factor that into the urgency of getting china, russia, japan, south korea -- all of us -- to stay on the same page, and to put as much effort into the denuclearization as possible. To have a nuclear weapon potentially in the hands of somebody like kim jong-un becomes more unacceptable. I want to move to the other headline, which is that of iran and robert levinson, the fbi agent who was reportedly working with the cia in iran. Disappeared seven years ago. His family has confirmed to abc news that he did have ties to the cia. His family said that the u.S. Government has abandoned and betrayed him and is getting lip service from the obama administration on their efforts for his release. Has there been any real progress? There hasn't been progress in the sense we don't have him back. But to suggest that we have abandoned him is simply incorrect and not helpful. The fact is, that I have personally raised the issue, not only at the highest level that i have been involved with, but also through other intermediaries. We don't have any meeting with anybody who has something to do with iran or approach to iran where we don't talk to them about how we'll be able to find not only mr. Levinson but we have two other americans that we're deeply concerned about -- do you have any -- we're working on several processes that I'm not free to talk about, but there are a number of different channels that are being worked and they're being worked aggressively. Do you believe that the iranian government is responsible for his disappearance? I believe the iranian government -- I can't tell you what happened. I think the iranian government has the ability to help us here. And we hope they will.

This transcript has been automatically generated and may not be 100% accurate.

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